Big banks have also cashed in on the return of volatility to Wall Street. The market drama, driven by Trump's trade crackdown as well as plunging tech stocks and fears about inflation, boosted trading activity as clients rushed to execute orders. That's a big moneymaker for Wall Street firms, which suffered from an unusually tranquil 2017.

"Last year was the best environment for investors and worst for trading desks. There was very little volatility," said Colas.

Trading revenue at Goldman Sachs(GS) soared 31% to a three-year high. Goldman Sachs rewarded its employees handsomely: the average worker made $110,000 during the first quarter, up from $96,500 last year.

"I wouldn't say we're popping champagne corks," Blankfein told CNBC on Wednesday, "but we can certainly see what happens when we start to walk back towards a normal financial market."

The news wasn't great for all big banks. Wells Fargo's stock dropped after the bank warned it faces a potential $1 billion penalty for auto and mortgage. The embattled bank warned it may need to revise its first-quarter earnings. Wells Fargo is also grappling with sanctions from the Federal Reserve that limit its asset size to $2 trillion.

One concern is that big banks are benefiting from powerful, but fleeting forces: volatility and tax cuts. The core business -- lending -- doesn't look as strong as some hoped given the strong economy and the positive impact of the corporate tax cuts.

For instance, JPMorgan said its commercial and industrial loans rose 5% from last year but were down 1% compared with the fourth quarter.

Marianne Lake, JPMorgan's chief financial officer, described during a call with analysts an "overall industrywide slowdown" in lending.

Lake said JPMorgan expects modest lending growth for 2018, but noted the bank is acting "very selective and cautious, given where we are in the cycle."

Another problem looming on the horizon: the bond market is acting up again. Short-term Treasury rates have jumped, while long-term rates are shrinking. That's known as a "flattening" yield curve and it's bad for banks, which pay interest on short-term rates and lend at long-term ones.

These dynamics help explain why investors aren't rushing to buy bank stocks right now. Colas said that despite their success, big banks are trading at roughly the same valuations as last year.

"While banks are earning very strong profits, investors are reluctant to reward them," he said.